Dual source analyzer with single detector

ABSTRACT

A dual source system and method includes a high power laser used to determine elements in a sample and a lower power device used to determine compounds present in the sample. An optical subsystem directs photons from a sample to a detector subsystem after laser energy from the laser strikes the sample along an optical path. After energy from the device strikes the sample protons are directed to the detector subsystem along the same optical path. The detector subsystem receives photons after laser energy from the laser strikes the sample and provides a first signal, and receives photons after energy from the device strikes the sample and provides a second signal. A controller subsystem pulses the high power laser and processes the first signal to determine elements present in the sample, energizes the lower power device and processes the second signal to determine compounds present in the sample.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/507,654 filed Jul. 17, 2012 and claims the benefit of andpriority thereto under 35 U.S.C. §§ 119, 120, 363, 365, and 37 C.F.R. §1.55 and § 1.78 and is incorporated herein by this reference.

FIELD OF THE INVENTION

The subject invention relates to spectroscopic instruments.

BACKGROUND OF THE INVENTION

Spectroscopic instruments are fairly well known. X-ray basedinstruments, for example, can be used to determine the elemental make upof a sample using x-ray florescence spectroscopy. Portable XRF hasbecome a preferred technique for elemental analysis in the field.Portable XRF is fast, non-destructive, and provides reasonably accurateresults (i.e., quantification of elemental concentrations in a widevariety of samples). With XRF, an x-ray tube is used to direct x-rays ata sample. Atoms in the sample absorb x-rays and re-emit x-rays that areunique to the atomic structure of a given element. A detector measuresthe energy of each x-ray and counts the total number of x-rays producedat a given energy. From this information, the types of elements and theconcentration of each element can be deduced. Commercially availableanalyzers include the Delta manufactured by Olympus NDT and the NitonXLT-3 manufactured by Thermo Fisher Scientific.

X-rays, however, pose a safety concern. Also, portable and benchtop XRFanalyzers have not to date measured beryllium (Be), boron (B), carbon(C), lithium (Li), oxygen (O), nitrogen (N), and the like.

Laser induced break down spectroscopy (LIBS) devices are known and usedto detect the elemental concentration of lower atomic numbered elementswith some accuracy. These devices typically include a high powered laserthat sufficiently heats a portion of the sample to produce a plasma. Asthe plasma cools, eventually the electrons return to their groundstates. In the process, photons are emitted at wavelengths unique to thespecific elements comprising the sample. The photon detection andsubsequent measurement of elemental concentrations are very similar tospark optical emission spectroscopy (OES). Examples of LIBS devices arethe LIBS SCAN 25 from Applied Photonics, the LIBS25000 from OceanOptics, and the RT 100 from Applied Spectra.

Still other instruments are better at determining the molecularcompositions present in a sample. Portable, laser based Ramanspectrometers or a wide bandwidth based (i.e., non-laser) near infra-red(NIR) analyzers can be used. These devices are configured to collecteither Raman spectra or infra-red absorption from a given sample. Theythen compare the acquired spectra to a library of spectra of purecompounds. From the comparisons, the devices then determine the majorcompounds present in the sample. The process of determining whatcombination of pure compounds spectra in published libraries yield themeasured spectrum of an unknown mixture is called chemometrics. Thereare several commercially available portable devices utilizing Ramantechnology including those manufactured by Thermo Fisher Scientific,Delta Nu and B&W Tek. For NIR, commercially available devices are madeby ASD, Thetino Fisher Scientific, and Spectral Evolution.

Portable Raman and NIR analyzers are able to identify compounds presentin a mixture, but they are generally limited to identifying what maincompounds are present (as opposed to how much of each compound ispresent), or, at best, they can provide an approximate quantification ofonly a few components in a mixture of compounds. This limitation is dueto sample response variation as a function of particle size, particledensity, and mixture type, whether it be a solid solution or aninhomogeneous mixture of compounds. These parameters can cause thespectrum from one material to be enhanced or reduced relative to theother materials to a fair extent. In addition, both the Raman and NIRmethods are sensitive to material very near the sample surface so thatany variation is bulk vs. surface concentrations will be missed. Evenwithout these effects, the ability to derive chemical constituents frommathematically combining spectra of pure compounds to simulate theunknown mixture spectrum rapidly degrades after the third compound, evenwith good quality spectra. In addition, currently available portableRaman and NIR units typically require a good deal of spectralinterpretation from the operator, thus limiting user community to moretechnical users.

It is also known to fuse the data in dual source systems. That is, forexample, Raman spectra data and LIBS spectra data are obtained andsoftware is configured to calculate probability values to pinpoint anunknown material like a microorganism. See for example, published U.S.Patent Application Nos. 2009/0163369 and 2011/0080577 and U.S. Pat. No.7,999,928 all incorporated herein by this reference. Some of thesedesigns are expensive and complex (using, for example, a FASTspectrometer and fiber optic bundles.)

Still, LIBS spectroscopy, for example, can produce inaccurate elementalconcentrations in some cases and Raman and NIR spectroscopy can reportone or more inaccurate compositions, mainly because for many compounds,the Raman or NIR spectra produced by those compounds are very similar.Plus, some libraries contain more than 10,000 spectra from the manycompounds. Fusing the data may not improve accuracy.

SUMMARY OF THE INVENTION

Featured is a novel portable (e.g., handheld, or easily transportablebenchtop or shoulder pack style) instrument that combines measurementfrom two technologies (e.g., LIBS and Raman or LIBS and NIR) with ananalysis algorithm that allows operators to quantify both elements andcompounds. Knowledge about the compounds present in the sample enablesthe method to better report the elemental concentrations. Knowledgeabout the elemental concentrations enables the method to better quantifythe compounds present.

In addition, the use of the LIBS measurement for elementalconcentrations allows a more refined searching of large libraries ofpure compound spectra used for NIR and Raman analysis. Therefore, thechemometrics process is also improved via a novel method since theelements present are measured in the sample from LIBS and only compoundscomprised of those measured elements can be present in the sample. Theknowledge of elemental concentrations thus greatly reduces and refinesthe library searches for Raman or NIR analysis.

Another unique feature of the method is that the analytical results areinternally consistent and satisfy expected mass balances and constraintequations. This means the total concentration of a given elementmeasured from LIBS will agree with the stoichiometric and molecularcomposition results from all the compounds that contain that element asdetermined by the Raman or NIR analysis.

Also, if trace compounds present in the sample are not detected in theRaman or NIR analysis, then detection of an element using LIBS andknowledge of other compounds actually detected by the Raman or NIRanalysis allows the reporting of the trace compounds.

Featured is a dual source system comprising a high power (e.g., LIBS)laser used to determine elements in a sample and a lower power device(e.g., Raman laser) used to determine compounds present in the sample.An optical subsystem is preferably configured to direct photons from thesample to a detector subsystem after laser energy from the high poweredlaser strikes the sample along an optical path and to direct photonsfrom the sample to the detector subsystem after energy from the lowerpowered device strikes the sample along the same optical path.

The detector subsystem may be configured to receive photons via theoptical subsystem from the sample after laser energy from the high powerlaser strikes the sample and provides a first signal. The detectorsubsystem also receives photons, via the optical subsystem, after energyfrom the lower powered device strikes the sample and provides a secondsignal.

A controller subsystem is preferably configured to pulse the high powerlaser and process the first signal to determine one or more elementalspresent in the sample and to energize the lower power device and processthe second signal to determine one or more compounds present in thesignal.

The optical subsystem may further be configured to directelectromagnetic energy from the lower power device to the sample alongan optical path including at least a portion of the optical path fromthe sample to the detector subsystem. The optical subsystem can also bedesigned to direct electromagnetic energy from the high power laser tothe sample along an optical path including at least a portion of theoptical path from the sample to the detector subsystem.

In one example, the lower power device outputs energy at a predeterminedwavelength and the optical subsystem includes an optical componentreceiving energy output by the lower power device and configured todirect said energy to the sample. The optical component may receivephotons from the sample and can be configured to filter wavelengths in anarrow band about a predetermined wavelength and to direct energy inwide bands above and below the narrow band to the detection subsystem.In one embodiment, the optical component includes a dichroic notchreflector configured to reflect energy from the lower power device tothe sample and to transmit energy in wide bands to the detectorsubsystem. Or, the reflector can be configured to transmit energy fromthe lower power device to the sample and to reflect energy in the widebands to the detector subsystem. One optical subsystem further includesa lens positioned such that photons from the sample after energy fromthe lower power energy device strikes the sample are received at andfocused by the lens. Photons from the sample after energy from the highpower device strike the sample are also received and focused by the samelens. The focusing lens can also be positioned to focus energy from thelower power device onto the sample.

In some examples, the controller subsystem is configured to determineone or more elemental concentrations in the sample based on the firstsignal and to quantify one or more compounds present in the sample basedthe one or more elemental concentrations determined to be present in thesample.

The controller subsystem can be further configured to adjust themeasured elemental concentrations based on the determined compounds. Inone example, determining one or more elemental concentrations includesusing one or more calibration constants and adjusting the elementalconcentrations includes using different calibration constants based onthe compounds present in the sample. Quantifying a compound in thesample can include using a concentration of an element unique to acompound in order to determine the concentration of the compound. Thecontroller subsystem can be further configured to compare the determinedelemental concentrations with elemental concentrations of the definedcompound concentrations using mass/balance equations. The controllersubsystem can also be configured to quantify concentrations usingelements shared among two or more compounds. Also, or in addition, thecontroller subsystem can be configured to report one or more additionalcompounds present in the sample based on the elemental concentrationsand the one or more determined compounds.

In some examples, the high power laser source is configured for LIBSspectroscopy and the lower power device is a laser configured for Ramanspectroscopy. In other examples, the lower power device is a nearinfrared source for near infra-red absorption measurements.

Also featured is a dual source system comprising a high power laser usedto determine elements present in a sample, a lower power device used todetermine compounds present in a sample, a detector subsystem configuredto receive photons from the sample, and an optical path from the sampleto the detector subsystem for the elemental determination the same asthe optical path for the compound determination. In some examples, anoptical path from the lower power device to the sample includes at leasta portion of the optical path from the sample to the detector subsystemand/or an optical path from the high power laser to the sample includesat least a portion of the optical path from the sample to the detectorsubsystem.

One dual source system includes a high power laser used to determineelements present in a sample, a lower power device used to determinecompounds present in a sample, a detector subsystem configured toreceive photons from the sample, and a first optical path from the highpower laser to the sample at least partially co-linear with a secondoptical path from the lower power device to the sample. In someexamples, an optical path from the sample to the detector subsystem isat least partially co-linear with the first and second optical paths.

Also featured is a method comprising directing photons from a sample,after impingement of high and low power energy at the sample, via thesame optical path from the sample to a detector subsystem and directinglower power energy to the sample via an optical path including at leasta portion of the optical path from the sample to the detector subsystem.The method may further include directing higher power energy to thesample via an optical path including at least a portion of the opticalpath from the sample to the detector subsystem.

Also featured is a method comprising directing lower power energy to asample via an optical path, directing high power energy to the samplevia an optical path at least partially co-linear with the optical pathfor the lower power energy, and directing photons from the sample afterimpingement of high and low power energy at the sample to a detectorsubsystem. The method may further include directing photons from thesample after impingement of high and low power energy at the sample viathe same optical path from the sample to the detector subsystem.

The subject invention, however, in other embodiments, need not achieveall these objectives and the claims hereof should not be limited tostructures or methods capable of achieving these objectives.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 shows a schematic three dimensional view showing an example of aportable handheld instrument in accordance with the invention;

FIG. 2A is a schematic block diagram showing the primary componentsassociated with the portable instrument of FIG. 1;

FIG. 2B is a block diagram of another example of the invention;

FIG. 2C is a block diagram of another example;

FIG. 2D is a block diagram depicting additional examples;

FIG. 3 is a flow chart depicting the primary steps associated with amethod in accordance with the invention and also associated with theprogramming of the microcontroller subsystem of FIG. 2; and

FIG. 4 is a schematic view showing a calibration method in accordancewith examples of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

FIG. 1 shows a version of a portable, hand held dual source device 10embodying an example of the invention. In one design, device 10 mayinclude separate belt or shoulder mounted power pack 12. Housing 14typically houses a high power laser 16, FIG. 2 used in a LIBS analysisto determine elemental concentration in sample 18. Lower power laser 20may be used in a Raman analysis to determine compounds present in sample18. Alternately, an NIR (infrared absorption) subsystem could be used.

Laser energy from laser 16 (e.g., 1064 nm) and energy from source 20(e.g., 785 nm) exit window 30 FIG. 1 via optics such as focusing lenses32 a and 32 h, FIG. 2 and also beam splitter 34. Photons from the sampleare returned to the device via the window 30 and are received atdetector subsystem 40 via beam splitter 34, lens 32 c, and notch filter42. A collimating optic 44, grating 46, and focusing optic 48 can beused to direct the photons to CCD detector array 50 which outputssignals to controller subsystem 52.

For LIBS analysis, the signals represent intensities at differentwavelengths defining the elements in the sample and the concentration ofeach of those elements. For a Raman (or NIR) analysis, the signalsresult from molecular group vibrations and are thus characteristic ofmolecular compounds present in the sample.

Various libraries may be stored in memory 54 accessed by controllersubsystem 52. Various mass balance equations, calibrations constants,and the like may also be stored in memory 54 as disclosed below.

Controller subsystem 52 may include one or more microprocessors, digitalsignal processors, or similar components, and/or application specificintegrated circuit devices, and may be distributed e.g., onemicroprocessor can be associated with the detector subsystem 40 whileanother microcontroller can be associated with the device's electroniccircuit board(s). The same is true with respect to the algorithms,software, firmware, and the like. The various electronic signalprocessing and/or conditioning and/or triggering circuitry and chip setsare not depicted in the figures.

In general, the processor subsystem 52 is configured (e.g., programmed)to pulse high power laser 16 and process the resulting signals fromdetector subsystem 40 to determine one or more elemental concentrationsin sample 18. Controller subsystem 52 then energizes lower power source20 and processes the resulting signals from detector subsystem 40 todetermine one or more compounds present in the sample. Knowing theelements present enables a more efficient determination of the compoundspresent. Then, based on the one or more compounds present in the sample,controller subsystem 52 can be configured to adjust the concentrationspreviously determined, although this step is optional. Finally,controller subsystem 52 is configured to quantify the one or orecompounds of the sample using the elemental concentration data. Knowingboth the elemental concentrations and compound concentrations enables amore accurate result.

In this particular design, the Raman laser delivery optics is combinedwith the spectrometer or detection subsystem optics while the LIBS laserdelivery optics are independent. Both measurements preferably use thesame detection subsystem for emission analysis.

The illuminated sample area during the Raman measurement is on the orderof 20-100 um while the plasma generated by the LIBS laser in on theorder of 1000 um or more. In order for the detection optics to beproperly aligned with the small Raman illumination area, it isadvantageous if they are co-linear and share the same focusing optics.In FIG. 2A it can be seen that if the sample is not perfectly located atthe focus of lens 32 b, light from a small illuminated area will stillmake it back to detection subsystem 40. On the other hand, if the samesample is out of position vertically, the LIBS laser 16 will hit thesample slightly offset from the detection optics focus. Since, however,the LIBS plasma is large (1 mm or so), portions of the plasma will stillbe within the detection optics view and make it to the detectorsubsystem 40 (e.g., a spectrometer).

Energy from laser 20 is directed toward optical component 34, typicallya dichroic notch reflector. Optical component 34 reflects only a narrowband of wavelengths including that of laser 20 (typically 785 nm).Optical component 34 directs collimated laser light through focusinglens 32 b to a small spot on the sample. The resulting Raman signal,shifted in the wavelength (e.g., 810-1040 nm), is emitted in alldirections from the sample. Light that intercepts lens 32 b isrecollimated. Since the Raman signals are wavelength shifted, they willpass through optical component 34 on toward detection subsystem 40passing through re-focusing lens 32 c and an optional notch filter 42designed to reject light in a narrow band surrounding the laserwavelength (e.g., 785 nm). The Raman signal is typically 6-9 orders ofmagnitude smaller than the excitation laser wavelength and so a similardegree of filtering may be required to prevent the laser signal fromoverwhelming the very small Raman signals.

Photons resulting after energy from laser 20 strikes the sample thuspass through optical component 34 in wide bands above and below thenarrow band filtered by component 34. In one example, component 34filters wavelengths in a narrow band of between about 760-780 nm. Ramanwavelengths from the sample 18 from about 790 to 1500 nm pass throughfilter 34.

The focus of lens 32 c directs the Raman light onto slit 41 of detectorsubsystem 40. The size of slit 41 is a function of the spectrometerresolution. Inside detection subsystem 40, the light passing the slit iscollimated by mirror 44 and then directed toward diffraction grating 46.The diffraction grating reflects the light such that each wavelengthleaves the grating at a slightly different angle. Focusing mirror 48causes each wavelength to be focused onto detector array 50 such thateach wavelength would be shifted to different segments of the detectorarray resulting in the measured spectrum. Other spectrometerimplementations are possible including Echell (with a 2D CCD),Paschen-Runge, and the like. A spectrometer which yields high resolutionover a wide band of wavelengths (e.g., 200 nm-1000 nm) is preferred.

During operation of LIBS laser 16, the Raman laser 20 is typicallyturned off and the LIBS laser 16 is pulsed in either a single burst ortrain of bursts. Light leaving the resulting generated plasma formed onsample 18 follows the same detection path namely lens 32 b, component34, lens 32 c, optional filter 42, and slit 41. LIBS wavelengths in thewide band ranges of about 180 nm-760 nm and about 780 nm-1500 nm aretransmitted by component 34. Plasma emissions in the narrow band arefiltered by component 34 and do not reach detection subsystem 40 butthis is such a small fraction of the available LIBS spectrum that it haslittle determent to the wealth of information available.

In another implementation, shown in FIG. 2B, wavelengths from the Ramanand LIBS laser are redirected (reflected) by component 34 as shown todetector subsystem 40 while the Raman laser is positioned such thatlaser energy is transmitted through optical component 34.

So far, the optical path from the sample to the spectrometer (alsocalled the return path) is the same for both the LIBS and Ramangenerated photons, the optical path from the Raman laser to the sampleincludes a portion of the optical path from the sample to thespectrometer, and the optical path from the LIBS laser to the sample isdirect to the sample.

Other embodiments can be enabled. In one example the optical path fromthe LIBS laser to the sample also includes a portion of the optical pathfrom the sample to the spectrometer.

FIG. 2C, for example, shows an embodiment where the return optical pathfrom the sample 18 to spectrometer 40 includes lens 32 b and low passfilter 55 which transmits all wavelengths below that of the LIBS laser16 (e.g., below about 1040 nm for a 1064 LIDS laser). Also included inthe return optical path is notch filter 57 which transmits wavelengthsexcept in a narrow band around the wavelength of the Raman laser 20.

The optical path for the Raman laser 20 includes notch filter 57 and lowpass filter 55 which reflects a narrow band surrounding the Ramanwavelength and directs this band to low pass filter 55 which transmitsthe narrow band to sample 18. So, the optical path for the Raman laser20 to the sample includes a portion of the return optical path.

The optical path for the LIBS laser includes low pass filter 55 whichreflects wavelengths above (e.g., above about 1050 nm) a wavelength nearthe wavelength (e.g., 1064) of LIBS laser 16 and directs them to sample18. Thus, the optical path for the LIBS laser now also includes aportion of the return optical path.

By choosing the correct filters, the positions of the spectrometer, theRaman laser and LIBS laser can vary as shown in the following chartreferring to FIG. 2D:

Configuration A B C D E 1 S RL LL NF LP 2 S LL RL LP NF 3 RL S LL BPF LP4 LL S RL HP NF 5 RL LL S 6 LL RL S

Key: S Spectrometer RL Raman Laser LL LIBS Laser NF Notch Filter BPFBand Pass Filter HP High Pass Filter LP Low Pass Filter

One preferred notch filter reflects light in a narrow band closelysurrounding the Raman wavelength and transmits approximately 100% ofwavelengths in wide bands above and below the narrow band. One preferredband pass filter transmits only a very narrow band closely surroundingthe Raman laser wavelength and reflects or otherwise filtersapproximately 100% of wavelengths in wide bands above and below thenarrow band. One preferred high pass filter transmits all wavelengthsabove a threshold (e.g., 1040 nm) and filters approximately 100% of allwavelengths below that threshold value. One preferred low pass filtertransmits all wavelengths below the threshold value and reflects orotherwise filters all wavelengths above the threshold. Other filters,thresholds, and bands could be used for other laser(s) or sourcewavelengths are within the scope of the subject invention.

By juxtapositioning all three beam paths (Raman laser excitation, LIBSlaser excitation, and spectrometer detection) at the output optics,several advantages are realized.

The juxtaposed geometry helps insure that the focus of the two lasersand spectrometer all occur at the same point on the sample.Additionally, this configuration is significantly more tolerant ofsamples slightly distanced from the ideal focal point. Also, LIBSmeasurements typically result in sample cratering and the superpositionof the Raman and LIBS spectrometer beam paths insure that the bottom ofthe crater can be continuously viewed regardless of depth. In all thedesigns discussed so far, additional filters and/or optical componentsmay be required for additional laser line rejection. Depending on thespectrometer type used, it may additionally contain a focusing lens tofocus the collimated beam onto a spectrometer slit.

A method of this invention, which can be implemented, for example, inthe device of FIGS. 1 and 2 as algorithms in software, typicallyincludes the steps depicted in FIG. 3. A LIBS measurement, step 60,measures the intensities of various wavelength of light from the variouselements in the sample. The LIBS measurement is very fast, typicallyrequiring a few microseconds of time. The laser 16, FIG. 2 is operatedin a pulsed mode meaning the laser is turned on for about 4 to 10 nsecto heat sample 18 and thus create a plasma, then switched off. At theend of the laser pulse, there is typically a 1 to 10 microsecond delaywhile the plasma cools and before the settling of the excited electronsback to their original atomic states occurs. After that delay, thedetection subsystem 40 begins acquiring atomic emission spectra. Thisspectral acquisition occurs for about another 1 to 2000 microsecondsafter which the LIBS measurement has concluded. Intensities at specificwavelengths that are characteristic of specific elements are measured atdetector subsystem 40, FIG. 2.

In step 62, FIG. 3 these intensities, adjusted for background levels,are converted into concentration values (W_(i) for element “I”)preferably from a universal calibration. In general, for opticalemission, the relation between concentration and measured lightintensity can be adequately represented by either a quadratic or cubicpolynomial. An example, for the case of measuring the element chromium(Cr) would be:W _(Cr) =K ₀ +K ₁ *I _(Cr) +K ₂ *I _(Cr) ²  (1)orK _(Cr) =K ₀ +K ₁ *I _(Cr) +K ₂ *I _(Cr) +K ₃ *I _(Cr) ³  (2)where W_(Cr) is the concentration of Cr in mass %, I_(Cr) is theintensity of light measured at the wavelength for chromium lightemission from the plasma, and K0, K1, K2, and K3 are calibrationcoefficients stored in memory 54, FIG. 2. These calibration coefficientsare determined from calibration where samples with known concentrations(W) at various levels are tested and the light intensity (I) emitted byeach element of interest is measured. The values of W versus I areplotted for each element, fitted by a quadratic or cubic polynomial,thus yielding the coefficients of the quadratic or cubic polynomial. Thecoefficients are the calibration constants used for that particular typeof sample. In this example, the type of sample may be the element Cr inan iron alloy type of sample.

In analytical measurements, the most accurate results are obtained whenthe calibration is tuned to the specific composition of the sample. Forexample, the best results when measuring Cr in an iron alloy is obtainedwhen the calibration factors K0, K1, etc. are derived from a calibrationusing iron alloys with known amounts of chromium. However, the fieldsample composition is generally unknown so the best calibrationcoefficients are not known a priori. Instead, based on the elements thatproduce the highest intensity of measured photons, the samplecomposition is estimated and the best available calibration factors areautomatically selected. If it is determined, for example that the sampleis a nickel alloy, then different calibration constants (e.g., K₀′, K₁′,K₂′, and K₃′) stored in memory are chosen at step 62.

Step 64, FIG. 3 in the method is to turn on the molecular excitationsource 20, FIG. 2 which is either a Raman laser or an NIR source (lamp),depending on whether the desired molecular measurement technique isRaman analysis or NIR absorption. During this time the LIBS laser 16 isallowed to regenerate so that a second LIBS pulse may be used later inthe measurement. Molecular spectra are acquired from the sample. Withknowledge of the compounds present, an improved estimate of the samplecomposition is now available. The controller subsystem can be configuredto use the compound information to choose a more optimal set ofcalibration coefficients K₀′, K₁′, etc., from memory for each element,therefore allowing more precise measurements.

In step 66, FIG. 3 a library search is initiated and in step 68 achemometrics process is used. Because of the complexity of thechemometrics process, thousands of similar spectra would have to beanalyzed and combined in such a way as to match the measured spectrumfrom the mixture. But here the LIBS measurement has determined the totalconcentrations of elements present in the sample. This knowledge isvaluable because it can be used in the searching algorithms to greatlylimit the number of spectra that need be search and analyzed by theRaman or NIR chemometrics process. For example, any library compound (inmemory 54, FIG. 2) can be ignored if it does not contain at least one ofthe elements measured by LIBS. This can greatly limit the number ofpossible compounds to consider in the chemometric analysis allowing fora more reliable determination of compounds present.

This is accomplished, for example, if a library search of either Ramanor NIR spectra finds spectra from two different compounds that match themeasured spectrum. However the compounds likely are comprised ofdifferent elements or different elemental concentrations. Because theLIBS measurement determines the elements present in the sample, one ofthe possible matches can be eliminated if that compound is comprised ofelements not found by the LIBS measurement or if the elementalconcentrations are significantly different. A good example is the casewhere LIBS measures total elemental concentrations Ca, Mg, C and O arepresent among others. An NIR measurement determines that the mineralcould either be Dolomite [formula is CaMg(CO₃)₂] or simple Calcite[formula is CaCo₃)]. Because the LIBS measurement detected anddetermines total Mg present, the mineral can be uniquely identified asDolomite because it contains Mg whereas Calcite does not.

With the compounds in the sample known, step 70, FIG. 3 is used torefine the choice of calibration coefficients for each element. In oneexample, in step 62, a default set of calibration constants K werechosen resulting in an output of 21% Cr. In step 68, the compoundchromium chloride (CrCl₃) was determined to be present in the sample.Based on this determination, a new set of calibration constants K′ areused resulting in an output of 19% Cr. In step 68, had the compoundsodium Chromate (Na₂CrO₄) been present, a different set of calibrationconstants K″ would have been automatically used resulting in 23% Cr.

One example of the calibration process is shown in FIG. 4. Forsimplicity a simple linear calibration is assumed, namely, W_(i)=K*I_(i)for element (i). In Table 1, column 1 is the name of the element beinganalyzed and column 2 is the measured intensity of light for thatelement, in arbitrary units, measured from the spectrometer. Column 3shows the result from Step 62, FIG. 3 where a general calibration isapplied. The general calibration is typically chosen from a data tablein memory 54, FIG. 2. The choice of calibration is dictated by whatelements were measured with the largest intensities. For example, if alarge amount of iron (Fe), silicon (Si) and oxygen (O) were measuredalong with other elements, then a calibration from an iron ore type ofmatrix would likely be chosen.

In steps 64-68, the Raman or NIR analysis is performed to determine whatcompounds are present in the sample at appreciable levels. The knownelemental content is used to guide the search of the material library,as mentioned earlier. From the knowledge of the major compounds, theelemental calibration can be further refined. For example it may bedetermined that one compound is appreciable higher in concentration thanothers. In the above example it may be determined that a large amount ofan organic compound or water is present. In this case there may be abetter choice of elemental calibration constants than previously used orthe calibration constants used must be corrected due to the presence ofa previously unknown compound. For the example in FIG. 4, it isdetermined that a correction (F) to the calibration constants willproduce a more accurate result. In this case, new calibration constants(K′) are generated by multiplying the initial choice (K) by thecorrection factor (F). Improved elemental concentration results are thengenerated and reported by multiplying the measured intensities (I) ofeach element by the associated calibration constants (K′). In mostcases, the adjusted calibration constant (K′) will change by 10-50%.

A further step in the method would be to re-cheek the Raman or NIRmaterials library to see if the revised elemental concentrationsdetermined from calibration constants K′ alter the results of materiallibrary search for compounds present. It is expected that the minorchanges to the elemental results will not impact the choice ofcompounds. If they do, then an iterative procedure can be used toeventually converge to a self-consistent result for both elementalconcentrations and compounds present.

Steps 72-76 show an approach which uses the results of the elementalconcentration data combined with the types of compounds present to yieldquantitative compound concentrations (P_(j)). Moreover, the elementaland compound concentrations can be analyzed to ensure internalconsistency, meaning mass balance equations are satisfied.

Steps 72-76 involve using the measured elemental concentrations fromLIBS (steps 62, 70) and the determined compounds from Raman or NIR (step68) to quantitatively determine the percentages of compounds present inthis sample. Moreover, mass balances are used to also assure that thetwo independent measurements of elemental concentrations (LIBS) andcompound concentrations (Raman or NIR) are self consistent. In mostcases, the resulting system of equations is over-determined meaningthere are more equations than unknowns. There may also be measurementuncertainties associated with each element measured by LIBS. This is adesirable outcome because standard mathematical techniques such as leastsquares can be used to find the best overall solution that meets themeasured elemental concentrations (including uncertainties), thecalculated compound concentrations and the stoichiometry associated withthese compounds, and the overall mass balance equations.

For example, suppose there are four compounds present in a sample asdetermined at step 68, FIG. 3: Compound A=SiO₂, Compound B=CaCO₃.Compound D=CH₂ and Compound E=Al₂O₃. Note that in practicality thecompounds SiO₂ and Al₂O₃ do not yield good NIR spectra but they areuseful in this case to teach the method. In addition there are threefree elements (free meaning they are not associated with any compound):Fe, Ni and Cu. The elemental concentrations are measured with LIBS andyields concentration values for all the elements present W_(Fe), W_(Ni),W_(cu), W_(Si), W_(O), W_(Ca), W_(C), W_(H), and W_(Al) step 62, FIG. 3.

The presence of the four compounds are determined by the Raman or theNIR measurement and the still unknown compound concentrations aredenoted by P_(A), P_(B), P_(D), and P_(E). The concentration of the freeelements Fe, Ni and Cu, and the concentration of the elements found onlyin one compound (Si, Ca, H and Al) are uniquely determined from the LIBSmeasurement. Here, the compounds in this example share two elementscarbon and oxygen (the shared elements). The LIBS measurement providestotal oxygen and total carbon concentration but it is not known from theLIBS measurement how much of the measured oxygen is in compound A, B orE. Similarly the LIBS measurement does not tell us how much of themeasured carbon is in B versus D. The NIR or Raman measurement onlyprovides presence of these compounds, but not concentrations.

In this example, each compound contains a unique element, meaning theelement isn't found in any of the other compounds determined to bepresent in the sample. Using stoichiometry, the percentages of compoundsA, B, D and E are given by:P _(A) =a*W _(Si),  (3)where a=(molecular weight of SiO₂)/(molecular weight of Si)/(number ofatoms of Si per atom of SiO₂).  (4)Here, the number of atoms of Si per atom of SiO₂ is equal to 1.

Also,P _(B) =b*W _(Ca),  (5)where b=(molecular weight of CaCO₃)/(molecular weight of Ca)/(number ofatoms of Ca per atom of CaCO₃).  (6)Here the number of atoms of Ca per atom of CaCO₃ is equal to 1.Similarly, P _(D) =d*W _(H),  (7)where d=(molecular weight of CH₂)/(molecular weight of H)/(number ofatoms of H per atom of CH₂).  (8)Here the number of atoms of H per atom of CH₂ is equal to 2.Finally, P _(E) =e*W _(Al)  (9)where e=(molecular weight of Al₂O₃)/(molecular weight of Al)/(number ofatoms of Al per atom of Al₂O₃).  (10)Here the number of atoms of Al per atom of Al₂O₃ is equal to 2.

At this point in the method, the self consistency test (mentioned above)can be performed by applying the overall mass balance equations. In thisexample, the weight percentages P where determined for the fourcompounds using measured values of elements that were unique to thecompound, i.e., elements not present in two or more compounds. The totalweight percent of carbon and oxygen are also known from the LIBSmeasurement. From a mass balance, the elemental concentration of totaloxygen, as measured by LIBS, must agree with the total oxygen expectedfrom the percentages and stoichiometry of compounds A, B and E. Also theelemental concentration of total carbon, as measured by LIBS, must agreewith the total carbon expected from the percentages and stoichiometry ofcompounds B and D. And, by definition the sum of all the compounds pluselements that are not molecularly bound in a compound must be 100%. Thefollowing mass balance equations ensue:W _(O) =f*P _(A) +g*P _(B) +h*P _(E)  (11)where f=(molecular weight of O)/(molecular weight of SiO₂)*(number ofatoms of O per atom of SiO₂),  (12)g=(molecular weight of O)/(molecular weight of CaCO₃)*(number of atomsof O per atom of CaCO₃), and  (13)h=(molecular weight of O)/(molecular weight of Al₂O₃)*(number of atomsof O per atom of Al₂O₃).  (14)Also,W _(C) =i*P _(B) +j*P _(D)  (15)where i=(molecular weight of C)/(molecular weight of CaCO₃)*(number ofatoms of C per atom of CaCO₃)  (16)where i=(molecular weight of C)*(molecular weight of CH₂)*(number ofatoms of C per atom of CH₂).  (17)Finally, P _(A) +P _(B) +P _(D) +P _(E) +W _(Fe) +W _(Ni) +W_(Cu)=100%  (18)

In this example, there are four unknowns (the concentrations of the fourcompounds) and there are seven equations including the mass balanceequations. Each measured value of elemental concentrations (W) from LIBSwill have a measurement uncertainty associated with it. There arestandard mathematical techniques utilizing the method of least squaresto solve over-determined systems of equations with statistical weights.

As another example, consider a sample with four compounds (CaS, CaSO₄,CaOH, and Fe₂O₃), plus several elements present only in the atomic form,(i.e., not part of a molecule) and iron (Fe) that is present both inatomic form in the sample and in the molecular form Fe₂O₃. This exampleis more complex than the previous because four elements measured by LIBSfor total concentration are shared across multiple compounds (Ca, S, Oand Fe). This example yields five unknown values and six equations. Thefive unknowns are the concentrations of the four compounds plus theconcentration of the atomic iron (i.e., the iron not bound in themolecule Fe₂O₃). The six equations are given by mass balances for Ca, S,O, Fe and H, plus the requirement that the sum of the concentrations ofall the compounds plus the elements in atomic form equals 100%.

In general, the solution will involve an over-determined system oflinear equations and measurement uncertainties, making least squareswith a convergence test after each iteration a favored approach.Provided there is at least one element that is unique to one of thecompounds in the sample, the problem will yield an over-determinedsystem of linear equations. In the first example, Si, Ca and Al were allunique to specific compounds in this example. In the second example,only hydrogen was unique.

Another example is a typical geochemical application. In this example,there are many metals in the sample and all reside in a mineralogicalform that a user seeks to learn. Suppose there are multiple metalspresent in a sample. The LIBS measurement determines concentrations forFe, Al. Si, Cu, Mg, Mn, C, H, N, O, Sr, Rb and Ti. The molecularmeasurement, likely NIR in this case rather than Raman, indicates thepresence of compounds Fe₂O₃, Al₂O₃, SiO₂, CuO, MgO, Mn₂O₅, CH₂N (using ahypothetical organic compound as a teaching example). The levels ofcompounds containing Sr, Rb and Ti are trace and not detected by the NIRbut the user knows they are there since the more sensitive LIBSmeasurement detected Sr, Rb and Ti. This example shows the power of thecombined measurements of molecular and elemental concentrations, alongwith an algorithm to handle the combined data set. The concentrations ofall the compounds detected by NIR can be determined from the LIBSmeasurement since the molecular form is known by the NIR measurement.There are additional equations for the organic compound because ituniquely contains H, C and N, all three of which are measured by totalelement concentration from LIBS. A mass balance on O yields an equation,and the requirement that the sum of all compounds and free elementconcentrations=100% yields a final equation. It is a safe assumptionthat the trace metals Sr, Rb and Ti are all in standard oxide form sincethe NIR measurement indicated oxide forms for all the other metals andthe LIBS measurement provided the total concentration of Sr, Rb and Ti.With the assumption of oxide form for Sr, Rb and Ti, the concentrationsof the compounds can be determined. Therefore, this is a system ofequations with 10 unknown compounds, but 14 equations. This system ofequations which is over-determined and with uncertainty weights on allthe measured values is a prime candidate for a least squaresminimization solution to the set of linear equations.

For example, it is well established that for portable Raman and NIRdevices, it is very difficult to determine the presence of compoundswith concentrations less than 0.5%. This is because these compounds makea very small contribution to the measured spectrum, since the measuredspectrum is an aggregate of spectra from the various compounds in thesample. However if a LIBS measurement identifies the presence of tracemetals that are not found in the compounds identified by the NIR orRaman measurement, then a finer analysis can be done using libraryspectra of only compounds containing those LIBS-detected elements. Thesearch could be limited to a specific class of such compounds, such asoxides only. As an example, consider a case where LIBS measurementmeasures the presence of elements Na, H, Mg, Li, C, O, Si, Fe, Mn. TheNIR measurement determines the only minerals present are Hectorite(containing Ma, Mg, Li, Li, O and H and iron oxide (Fe₂O₃). Then, it canbe reasonably assumed that there are low levels K- and Mn-containingcompounds present in the sample, likely K₂O and MnO. Those libraryspectra can be folded into the chemometrics process.

In step 78, FIG. 3 the concentration data is reported and stored. It istypical in most measurements, including LIBS, that performing a secondcycle of a LIBS test, followed by an NIR or Raman test, will improve theprecision of the measurement. Thus in step 80, the software will examinethe current result, compared to the previous result, and either repeatthe result or terminate the test depending the settings chosen by theoperator, step 82.

In summary, one novel approach is to quantify both elements andcompounds with a single preferably portable device by first measuringwith LIBS to determine all elements present (using an assumedcalibration) based on the relative intensities of elements measured,then performing a Raman or NIR test to determine what compounds arepresent, using the known elements from the LIBS measurement to refinethe library search to improve the accuracy of compound determination,and, based on the knowledge of the major compounds, solve a system of(typically) over determined equations including mass balances todetermine percentages of compounds, and possibly further refining thecalibrations for the elemental analysis now that percentages ofcompounds are known. This solution process can be iterative until allthe equations are satisfied.

There are other embodiments that can be envisioned as well. Portable XRFcould be used to measure elemental concentrations instead of LIBS.However, XRF analysis is difficult for elements with atomic numbers lessthan Mg, and therefore C, O, N, Be, B and other common elements will notbe measured. Also, the Raman or NIR measurement can be taken first,followed by the LIBS measurement. The combined LIBS+NIR or LIBS+Ramanmeasurements can be taken once, meaning a single LIBS test of the samplefollowed by a Raman or NIR test, or multiple tests of each are possible.In general, multiple tests improve precision especially of the LIBSresult but there is a point of diminishing returns where additionalrepeat tests do not appreciably improve the result.

Thus, featured via the steps of FIG. 3 is a computer implemented methodcomprising analyzing emission spectra from a sample to determine one ormore elemental intensities at different wavelengths. The concentrationof one or more elements present in the sample is calculated using thefirst set of calibration data. A molecular measurement technique isemployed to determine one or more compounds present in the sample usingthe one or more elements deter mined to be in the sample. Based on theone or more compounds determined to be present in the sample, theconcentrations of the one or more elements can be recalculated using anoptional second set of calibration data. Based on the recalculatedconcentrations of the elements, and the compounds present in the sampleare quantified. Mass balance equations can be used to recalculate theconcentration of the elements and compounds. Also, one or moreadditional compounds can be reported based on trace elements determinedto be in the sample and the other compounds found to be in the sample.

So, although specific features of the invention are shown in somedrawings and not in others, this is for convenience only as each featuremay be combined with any or all of the other features in accordance withthe invention. The words “including”, “comprising”, “having”, and “with”as used herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments.

In addition, any amendment presented during the prosecution of thepatent application for this patent is not a disclaimer of any claimelement presented in the application as filed: those skilled in the artcannot reasonably be expected to draft a claim that would literallyencompass all possible equivalents, many equivalents will beunforeseeable at the time of the amendment and are beyond a fairinterpretation of what is to be surrendered (if anything), the rationaleunderlying the amendment may bear no more than a tangential relation tomany equivalents, and/or there are many other reasons the applicant cannot be expected to describe certain insubstantial substitutes for anyclaim element amended.

Other embodiments will occur to those skilled in the art and are withinthe following claims.

What is claimed is:
 1. A dual source handheld analysis systemcomprising: a high power laser used to determine elements in a sample; alower power device used to determine compounds present in the sample; anoptical subsystem including optical components and configured to: directphotons from the sample to a detector subsystem after laser energy fromthe high powered laser strikes the sample along an optical path, directphotons from the sample to the detector subsystem after energy from thelower powered device strikes the sample along said same optical path,direct photons from the high power laser to the sample via at least aportion of said optical path, direct photons from the lower power deviceto the sample via at least a portion of said optical path, and thedetector subsystem configured to: receive photons via the opticalsubsystem from the sample after laser energy from the high power laserstrikes the sample and providing a first signal, and receive photons viathe optical subsystem after energy from the lower powered device strikesthe sample and providing a second signal; and a controller subsystemconfigured to: pulse the high power laser and process the first signalto determine one or more elements present in the sample, and energizethe lower power device and process the second signal to determine one ormore compounds present in the sample.
 2. The system of claim 1 in whichthe lower power device outputs energy at a predetermined wavelength andthe optical subsystem includes an optical component receiving saidenergy at said predetermined wavelength output by the lower power deviceand configured to direct said energy at said predetermined wavelength tothe sample.
 3. The system of claim 2 in which said optical componentfurther receives photons from the sample and is configured to filterwavelengths in a narrow band about said predetermined wavelength and todirect energy in wide bands above and below said narrow band to saiddetection subsystem.
 4. The system of claim 3 in which said opticalcomponent includes a dichroic notch reflector.
 5. The system of claim 4in which said reflector is configured to reflect energy from the lowerpower device to said sample and to transmit energy in said wide bands tosaid detector subsystem.
 6. The system of claim 4 in which saidreflector is configured to transmit energy from the lower power deviceto said sample and to reflect energy in said wide bands to said detectorsubsystem.
 7. The system of claim 1 in which said optical subsystemfurther includes a lens positioned such that photons from the sampleafter energy from the lower power energy device strike the sample arereceived at and focused by said lens and photons from the sample afterenergy from the high power device strikes the sample are received andfocused by said lens.
 8. The system of claim 7 in which said focusinglens is also positioned to focus energy from the lower power device ontothe sample.
 9. The system of claim 1 in which said controller subsystemis configured to determine one or more elemental concentrations in thesample based on the first signal.
 10. The system of claim 9 in whichsaid controller subsystem is further configured to quantify one or morecompounds present in the sample based the one or more elementalconcentrations determined to be present in the sample.
 11. The system ofclaim 10 in which the controller subsystem is further configured toadjust the measured elemental concentrations based on the determinedcompounds.
 12. The system of claim 11 in which the determining one ormore elemental concentrations includes using one or more calibrationconstants and adjusting the elemental concentrations includes usingdifferent calibration constants based on the compounds present in thesample.
 13. The system of claim 10 in which quantifying a compound inthe sample includes using a concentration of an element unique to saidcompound to determine the concentration of said compound.
 14. The systemof claim 10 in which the controller subsystem is further configured tocompare the determined elemental concentrations with elementalconcentrations of the defined compound concentrations.
 15. The system ofclaim 14 in which the comparison includes using mass/balance equations.16. The system of claim 10 in which the controller subsystem isconfigured to quantify concentrations using elements shared among two ormore compounds.
 17. The system of claim 10 in which the controllersubsystem is configured to report one or more additional compoundspresent in the sample based on the elemental concentrations and the oneor more determined compounds.
 18. The system of claim 1 in which thehigh power laser source is configured for LIBS spectroscopy.
 19. Thesystem of claim 1 in which the lower power device is a laser configuredfor Raman spectroscopy.
 20. The system of claim 1 in which the lowerpower device is a near infrared source for near infra-red absorptionmeasurements.
 21. A dual source handheld analysis system comprising: ahigh power laser used to determine elements present in a sample; a lowerpower device used to determine compounds present in a sample; a detectorsubsystem configured to receive photons from the sample; an optical pathfrom the sample to the detector subsystem for the elementaldetermination the same as the optical path for the compounddetermination; and an optical path from the high power laser and thelower power device to the sample including at least a portion of theoptical path from the sample to the detector subsystem.
 22. The systemof claim 21 in which the optical path from the sample to detectorsubsystem includes a first lens and a notch filter.
 23. The system ofclaim 22 in which an optical path from the lower power device to thesample includes the notch filter positioned to direct energy from thelower power device to said first lens.
 24. The system of claim 23 inwhich said optical path from the sample to the detector subsystemincludes said filter positioned to direct wavelengths in wide bandsabove and below a narrow band to the detector subsystem.
 25. The systemof claim 21 further including a controller subsystem configured todetermine one or more elements present in the sample after energy fromthe high power laser strikes the sample and to determine one or morecompounds present in the sample after power from the lower power devicestrikes the sample.
 26. The system of claim 25 in which the controllersubsystem is further configured to determine elemental concentrationsand to quantify one or more compounds present in the sample based on thedetermined elemental concentrations in the sample and the determinedcompounds present in the sample.
 27. The system of claim 21 in which thehigh power laser source is configured for LIBS spectroscopy.
 28. Thesystem of claim 21 in which the lower power device is a laser configuredfor Raman spectroscopy.
 29. The system of claim 21 in which the lowerpower device is a near infrared source for near infra-red absorptionmeasurements.
 30. A dual source handheld analysis system comprising: ahigh power laser used to determine elements present in a sample; a lowerpower device used to determine compounds present in a sample; a detectorsubsystem configured to receive photons from the sample via a firstoptical path; and a second optical path from the high power laser to thesample at least partially co-linear with a third optical path from thelower power device to the sample, the second and third optical pathsincluding at least a portion of the first optical path.
 31. The systemof claim 30 in which the third optical path from the lower power deviceto the sample includes a notch filter positioned to direct energy fromthe lower power device to a first lens.
 32. The system of claim 31 inwhich said first optical path from the sample to the detector subsystemincludes said filter positioned to direct wavelengths in wide bandsabove and below a narrow band to the detector subsystem.
 33. The systemof claim 30 further including a controller subsystem configured todetermine one or more elements present in the sample after energy fromthe high power laser strikes the sample and to determine one or morecompounds present in the sample after power from the lower power devicestrikes the sample.
 34. The system of claim 33 in which the controllersubsystem is further configured to determine elemental concentrationsand to quantify one or more compounds present in the sample based on thedetermined elemental concentrations in the sample and the determinedcompounds present in the sample.
 35. The system of claim 30 in which thehigh power laser source is configured for LIBS spectroscopy.
 36. Thesystem of claim 30 in which the lower power device is a laser configuredfor Raman spectroscopy.
 37. The system of claim 30 in which the lowerpower device is a near infrared source for near infra-red absorptionmeasurements.
 38. A dual source handheld analysis system comprising: ahigh power laser used to determine elements in a sample and emitting alaser beam directed to a sample via a lens; a lower power device used todetermine compounds present in the sample and emitting a beam directedto the sample via said lens; an optical subsystem configured to: directphotons from the sample to a detector subsystem after laser energy fromthe high powered laser strikes the sample along an optical pathincluding said lens; and direct photons from the sample to the detectorsubsystem after energy from the lower powered device strikes the samplealong said optical path including said lens; the detector subsystemconfigured to: receive photons via the optical subsystem from the sampleafter laser energy from the high power laser strikes the sample andproviding a first signal, and receive photons via the optical subsystemafter energy from the lower powered device strikes the sample andproviding a second signal; and a controller subsystem configured to:pulse the high power laser and process the first signal to determine oneor more elements present in the sample, and energize the lower powerdevice and process the second signal to determine one or more compoundspresent in the sample.